If I eat a sugary snack on an empty stomach my blood glucose level will quickly drop into the critical low range. I’ll get light headed and have slow down or sit down until my blood glucose returns back to normal (takes just a few minutes).
I learned this the hard way by eating a Cliff Bar just before jogging. Also one time I was hungry just before work and so I ate a granola bar and soon I felt weird. I worked in a clinical lab at the time. I had my blood drawn and I tested the blood glucose and it was 39 mg/dL.
I have no idea why my pancreas over react like this (dumping too much insulin into my bloodstream). I manage it by staying away from high sugar foods.
Also at the clinical lab where I worked a blood glucose less that 50mg/dL was considered critical.